Spot beam satellites are effective for the transmission and reception of unicast and multicast data. In typical spot beam satellites, many smaller spot beams are used to provide coverage for a larger area that is defined by the union of the areas covered by each of the smaller spot beams. An example is depicted in FIGS. 1A-1C, which show how a number of spot beams, such as individual spot beam 102, provide satellite coverage over a large coverage area 104.
FIG. 2 is a simplified diagram of a forward link of a typical bent pipe spot beam satellite system using a hub-spoke architecture. The depicted hardware connects one user beam 224 (or spot beam) to a gateway (GW) terminal 207 in a GW beam 208. The GW terminal 207 transmits data through a satellite 206 down to a plurality of user terminals (UT's) 226 in the user beam 224. The satellite 206 in this example is simplified but shows key elements of one forward link signal pathway including a receive (Rx) antenna 212, a low noise amplifier (LNA) 214, a frequency converter 216, a high power amplifier (HPA) 218, and a transmit (Tx) antenna 220. Many UT's 226 can operate in the same user beam 224 and receive data from a single GW transmission 210 via multiplexing of the data into a single aggregated downlink signal 222 (e.g., time division multiplexing (TDM), frequency divisional multiplexing (FDM), and the like). Typically each UT only processes the data in the stream that is addressed to itself. A typical satellite 206 can have a number of these sets of pathway hardware connecting a number of GW's to a number of user beams.
Some conventional spot beam satellites replace the HPA 218 shown in FIG. 2 with a multi-port amplifier (MPA). As shown in FIG. 3, a MPA can include a hybrid matrix (HM) 332, HPA's 318a, 318b, 318N, and an inverse hybrid matrix 334. This configuration can provide a higher power HPA by using several HPA's 318a, 318b, 318 N in parallel. When used in this manner, an input signal s(t) is applied to one input port, and all other inputs are terminated (no input signal). The output signal y(t) is present on the first output port, and all other ports are terminated with essentially no signal present. The motivation is to make a higher power HPA by combining N HPA's. In this configuration, the MPA can be used to increase transmit power to a single user beam.
Another conventional use of a MPA is depicted in FIG. 4, which shows a HM 432, HPA's 418a, 418b, 418 N, and an inverse hybrid matrix 434. As shown in this figure, the N input signals s1(t) . . . sN(t) are different data streams with the content of each stream targeted for different sets of UT's in different spot beams. The input signals sj(t) . . . sN(t) may originate, for example, from different GW terminals. The output signals y1(t) . . . yN(t) are amplified versions of the input signals. Different data content is provided to each of the N beams. In this configuration, the MPA can be used to share total transmit power amongst the distinct user beams.
A single user beam 224, as shown in FIG. 2, typically covers a small subset of a desired coverage area. Many user beams are employed in a manner similar to that depicted in FIG. 1 to provide service to a larger coverage area. Each of the user beams is serviced by a GW, and a number of user beams may be serviced by the same GW by use of different frequencies and/or polarizations. The total coverage area is the union of the areas covered by the individual user spot beams. This coverage area is the region where satellite service can be offered to customers. This coverage area is fixed and is selected during a satellite design process.
Satellite procurement, design, construction, launch, and test is a lengthy process. This process typically takes up to four years or more. The coverage area must be specified very early on in this process. In many instances, the desired coverage area is not well known at these early stages of satellite design. An educated guess must be made as to where the best coverage areas might be. If one chooses incorrectly, a coverage area may be selected that has few potential customers. This is clearly an undesirable consequence.
This problem is further complicated by the long operational lifetime of satellites. Satellites typically have an operational lifetime of 15 years or more. During this time, target services areas can change dramatically. This can occur due to the development of ground infrastructure (e.g., wireless and fiber network build outs), re-purposing of the satellite, movement of the satellite to a different orbit slot, and the like. The satellite spot beams, however, and thus the coverage areas, are fixed in location and typically cannot be modified despite these changes.
Further, offered load at different spot beams can vary dramatically over short time periods. For example, a satellite system that covers the continental United States may experience busy hours on the East Coast that correspond to non-busy hours on the West Coast.
Thus, there is a need for improved spot beam satellites that allow for modification of capacity and coverage areas to adjust to short term demands and also throughout the operational lifetime of the satellite.